Method for controlling the starting of an internal combustion engine

ABSTRACT

The invention relates to the starting of an internal combustion engine. The engine is coupled to an exhaust aftertreatment device that has a minimal threshold temperature for proper operation. Within a certain period of time after engine start, the load on an electrical generator driven by the engine is increased. Also, the air intake is throttled to reduce the intake manifold pressure to a target pressure. Both measures provide faster engine and catalyst warm-up and, thus, reduced emissions, particularly for a diesel engine in connection with an oxidation catalyst.

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for controlling thestarting of an internal combustion engine comprising an exhaustaftertreatment device that requires a minimal threshold temperature forproper operation. Moreover, the invention relates to a system comprisingan internal combustion engine, an exhaust gas aftertreatment device, anelectrical generator, and an engine controller.

[0003] 2. Background and Summary of the Invention

[0004] During the last few years, regulations for the protection of theenvironment have become increasingly stringent. This makes it more andmore difficult to meet legal requirements, though exhaust aftertreatmentdevices like three-way catalysts, conventional oxidation catalysts, andparticulate filters are standard today.

[0005] According to a first aspect of the invention, a method forcontrolling the starting of an internal combustion engine is provided.The engine is coupled to an exhaust aftertreatment device that has aminimal threshold temperature for proper operation. During a certainperiod of time after engine start, the following steps are performed: a)increasing the electrical load of an electrical generator that is drivenby the engine; and b) throttling the air intake to reduce the intakemanifold pressure to a target pressure.

[0006] During warm-up of the engine, the aftertreatment device ispossibly cold and, therefore, not at its optimal working range orpossibly not operative at all. Exhaust gases are therefore released intothe atmosphere essentially untreated. This leads to high emissionsduring engine start, which represent a considerable fraction of thetotal emissions of the internal combustion engine. An advantage of thepresent method is a considerable reduction in emissions of the internalcombustion engine by focusing on the starting period of the engine.

[0007] The method according to the present invention causes additionalpower to be consumed by the loads that are coupled to the generator.This leads to a higher load for the engine which, in turn, results infaster warm-up of the exhaust gases. Thus, the period of time duringwhich the aftertreatment device is not operative is reduced. Throttlingcontributes further to this effect because throttling air flow throughthe engine means that less mass has to be heated with a given amount ofenergy, yielding higher combustion temperatures in the cylinders.Furthermore, efficiency of the engine is reduced, partially due to anincrease in pumping losses. A higher fuelling rate is used to providethe desired torque, thus leading to a higher temperature of the exhaustgases.

[0008] The electrical loads that are coupled to the generator preferablycomprise electrical consumers that are present in a vehicle anyway,e.g., at least one glow plug of the engine or an electrical heater ofthe cabin or the windshield. The advantage of said consumers is thattheir short-term operation as additional load will not be noticed by thedriver.

[0009] According to another aspect of the invention, exhaust gasrecirculation is reduced or stopped during throttling. Due to thereduction of the intake manifold pressure, the pressure differencebetween intake manifold and exhaust manifold increases, which may leadto an excessive amount of exhaust gas recirculation. This excessiveexhaust gas recirculation is prevented by reducing or stopping exhaustgas recirculation, i.e., by closing the exhaust gas recirculationvalves.

[0010] If a turbine with variable geometry is present in the engine, itmay be operated open-loop only during throttling. This preventsturbocharger over-speed which might result from throttling the intakewhile attempting to stabilize intake manifold pressure.

[0011] Preferably, the desired exhaust temperature is attempted byincreasing electrical load on the generator alone. If this does notsucceed, however, throttling is also carried out. The decision toinclude throttling is preferably based on the exhaust temperaturedownstream of the aftertreatment device. Thus, throttling is carried outif the exhaust gas temperature downstream of the aftertreatment deviceis below a given threshold temperature.

[0012] The goal of the method, according to the present invention, is toreach a temperature of the exhaust gas that is above the thresholdtemperature for proper operation of the aftertreatment device as soon aspossible after starting the engine. Consequently, increasing theelectrical load and throttling are preferably stopped if the exhaust gastemperature has reached this threshold, thus limiting the time spentwithin the exceptional engine mode of steps a) and b).

[0013] To avoid undesirable implications of increasing electrical loadon the generator and throttling, they are preferably carried out onlywhen the temperature of the engine at start is within a certaintemperature interval, i.e., not too high and not too low.

[0014] Preferably, the combustion engine is a diesel engine and theaftertreatment device comprises an oxidation catalyst. Presently, dieselengines emit most of their cycle emissions of CO and HC during engineand catalyst warm-up. The oxidation catalyst does not convert the CO andHC leaving the engine until it has reached a temperature of about 200°C. Therefore, the advantages of the present invention are most prominentin conjunction with such a diesel engine and an oxidation catalyst.Here, a considerable reduction in total emissions can be achieved.

[0015] The above advantages and other advantages, objects, and featuresof the present invention will be readily apparent from the followingdetailed description of the preferred embodiments when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0016] The advantages described herein will be more fully understood byreading an example of an embodiment in which the invention is used toadvantage, referred to herein as the Detailed Description, withreference to the drawings wherein:

[0017]FIG. 1 shows a flowchart of a method to control the starting of aninternal combustion engine according to the principles of the presentinvention.

DETAILED DESCRIPTION

[0018] The inventive method provides rapid increase in the exhaust gastemperature after engine start to improve catalyst performance. Themethod will be described with reference to a preferred implementationthat comprises a diesel engine equipped with an exhaust gasrecirculation (EGR) system, an intake air throttle, an oxidationcatalyst, and a temperature sensor downstream of that catalyst.Moreover, the engine comprises an engine control unit (ECU), which isprogrammed with the necessary software to execute the inventivealgorithm. The algorithm is executed as part of the overall enginecontrol strategy at a fixed sampling rate, e.g., once every 16 ms.

[0019] Referring to FIG. 1, the algorithm beings in block 10. Controlpasses to block 11 in which the ECU initializes a timer, t_start, tozero, in block 11.

[0020] If the engine coolant temperature, ECT, is not within a range[ECT_min, ECT_max], the algorithm is terminated in block 12 to minimizeimpact on drivability and performance. ECT_min and ECT_max arecalibratable.

[0021] If the engine coolant temperature, ECT, is within said range, thealgorithm checks in block 13 the catalyst outlet temperature, T_exh. IfT_exh is below a first predetermined threshold, T_exh_min_(—)1, forexample, 200° C., electrical loads are switched on in block 14 to placea higher load on the engine and thus increase engine out exhaust gastemperature. Preferably, the loads which are switched on are those thatare not noticeable by the driver such as a windshield heater or glowplugs.

[0022] Once the exhaust gas temperature exceeds the first thresholdT_exh_min_(—)1, the electrical loads are switched back to their defaultor driver selected values.

[0023] Next, the algorithm checks in block 15 whether the catalysttemperature T_exh is below a second calibratible thresholdT_exh_min_(—)2, for example, 150° C. If so, the additional electricalloads will not raise the exhaust gas temperature sufficiently and theintake throttling feature is activated in block 16. The intake throttleis used to lower the intake manifold pressure (MAP) to a targetpressure, MAP_ref, which is a function of speed and load. During thisthrottling, the EGR valve is closed and the variable geometry turbine(VGT) is operated in open loop control only.

[0024] The algorithm is terminated in block 17 or 18 after acalibratible period of time, t_max.

[0025] In an alternative embodiment without an exhaust gas temperaturesensor, the checks on T_exh_min_(—)1 and T_exh_min_(—)2 of blocks 13 and15 are not performed. The algorithm is executed until the timer hasreached the maximum value t_max.

[0026] While several modes for carrying out the invention have beendescribed in detail, those familiar with the art to which this inventionrelates will recognize alternative designs and embodiments forpracticing the invention. The above-described embodiments are intendedto be illustrative of the invention, which may be modified within thescope of the following claims.

We claim:
 1. A method for controlling the starting of an internalcombustion engine an exhaust aftertreatment device with a minimalthreshold temperature for proper operation, wherein the method isperformed within a predetermined time period after engine start, themethod comprising: increasing an electrical load on an electricalgenerator that is driven by the engine; and throttling an air intake ofthe engine to reduce an intake manifold pressure to a target pressure.2. The method of claim 1 wherein the electrical load of said generatorcomprises at least one glow plug disposed in the engine.
 3. The methodof claim 1 wherein the electrical load of said generator comprises anelectrical heater.
 4. The method of claim 1 wherein the engine has anexhaust gas recirculation system in which exhaust gases are conductedfrom an engine exhaust to an engine inlet via an exhaust gasrecirculation valve, further comprising reducing a quantity of exhaustgases recirculated in response to said throttling.
 5. The method ofclaim 1 wherein the engine has a variable geometry turbine coupled to anair inlet of the engine, further comprising operating said turbine withopen-loop control in response to said throttling.
 6. The method of claim1 wherein said throttling is discontinued when a gas temperaturedownstream of the aftertreatment device is below a thresholdtemperature.
 7. The method of claim 1, further comprising: discontinuingsaid increasing and said throttling when an exhaust gas temperaturedownstream of the aftertreatment device is greater than said thresholdtemperature for proper operation of the aftertreatment device.
 8. Themethod of claim 1 wherein said increasing the electrical load and saidthrottling are carried out only when a temperature of the engine iswithin a predetermined temperature interval.
 9. A system for controllingan internal combustion engine, the engine having an exhaust gasaftertreatment system, an electrical generator coupled to the engine,and a throttle valve disposed in an inlet of the engine, the systemcomprising: an engine controller, the controller increasing anelectrical load on the electrical generator, the controller furtherclosing, partially, the throttle valve.
 10. The system of claim 9wherein said throttle closing causes a pressure in the engine intake toreduce to a target pressure.
 11. The system of claim 9 wherein theengine is a diesel engine.
 12. The system of claim 9 wherein theaftertreatment device is an oxidation catalyst.
 13. The system of claim9, further comprising an exhaust gas recirculation system in whichexhaust gases are conducted from an engine exhaust to an engine inletvia an exhaust gas recirculation valve coupled to said controller,wherein said controller causes an amount of flow through said exhaustgas recirculation valve to reduce in response to said throttle closing.14. The system of claim 9 wherein said controller causes said throttleclosing is accomplished when an exhaust gas temperature downstream ofthe exhaust aftertreatment device is below a threshold temperature. 15.The system of claim 8, further comprising glow plugs disposed in enginecylinders wherein said electrical load is placed on said electricalgenerator by said glow plugs.
 16. The system of claim 8, furthercomprising an electrical heater disposed in a vehicle in which theengine is also disposed where said electrical load is placed on saidelectrical generator by said glow plugs.
 17. A method for controlling aninternal combustion engine driving an electrical generator, the enginehaving an exhaust aftertreatment device disposed in an engine exhaust,the engine also having a throttle valve disposed in an engine inlet, themethod comprising: increasing an electrical load placed on theelectrical generator; and closing, partially, the throttle valve. 18.The method of claim 17 wherein said throttle closing is accomplished toprovide a target pressure in the engine inlet.
 19. The method of claim17 wherein said increasing and said closing are performed with apredetermined time period after the engine is started.
 20. The method ofclaim 17 wherein said engine aftertreatment device is an oxidationcatalyst having a minimum threshold temperature for proper operation.